Method and apparatus for emissions detection in a combustion appliance

ABSTRACT

A furnace system that generates heat by combustion is provided. The furnace system includes a sensor ( 100 ) that detects a gas concentration. The sensor is in communication with the flue gas ( 15 ). A controller is in communication with the sensor. The controller monitors the gas concentration and acts to control or deactivate the furnace.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to furnaces and, more particularly, amethod and apparatus for detecting incomplete combustion in a furnace.

2. Description of the Related Art

Generally, complete combustion is the reaction between a hydrocarbon andoxygen that results in the formation of water vapor and carbon dioxideto release heat. A combustion reaction in which carbon monoxide (CO) isformed from a hydrocarbon is incomplete combustion or partialcombustion. Incomplete combustion occurs when there is an insufficientamount of oxygen to react with the hydrocarbon resulting in CO, apoisonous gas. CO is also formed from other factors such as quenching acombustion process. Furnace systems are designed to run the combustionreaction with an excess of oxygen so that complete combustion can takeplace and the maximum amount of heat may be released from thehydrocarbon fuel. Therefore, incomplete combustion is undesirable in afurnace system that uses combustion to generate heat. In addition,incomplete combustion can adversely affect the function of the furnacesystem, such as, for example, decreasing efficiency.

Currently, residential furnaces do not have a detection system fordirectly monitoring the concentration of carbon monoxide or other gassespresent in combustion products due to feasibility including high cost.Pressure switches provide a mechanism to ensure proper airflow infurnaces. The pressure switches are only activated when the properamount of airflow is reached. In an event the minimum amount of airflowis not reached the furnace shuts down. In the furnace system, thepressure switches, undesirably, only deactivate the furnace system ifthere is an air blockage or starvation of combustion air.

Commercially available sensors, generally, are not used in fuel-firedfurnaces due to the high cost of the sensor technology. Newly developedCO sensors are smaller and less expensive so they are better suited inthis regard. Oxygen, carbon dioxide and hydrocarbon gas sensors are alsofunctional for the purposes of detecting incomplete combustion.Temperature in furnaces can cause sensor failure. Excessivetemperatures, such as temperatures greater than about 550° F., can causesensor damage and failure. Tubing or sample pumps may be used to removesensors from harsh temperature and humidity conditions.

Accordingly, there is a need for an improvement in applying sensors thatdetect incomplete combustion in a furnace.

SUMMARY OF THE INVENTION

A furnace system that generates heat by combustion is provided. Thefurnace system includes a sensor that detects a gas concentration of aflue gas. The sensor is in communication with the flue gas. A controlleris in communication with the sensor. The controller monitors the gasconcentration. A baffle plate directs a first portion of the flue gasinto contact with the sensor and a second portion of the flue gas in adirection away from the sensor. A draft safeguard switch port has adraft safeguard switch that selectively permits dilution air to enterthe furnace system to mix with the first portion of the flue gas.

In another aspect, a furnace system that generates heat by combustion isalso provided. The furnace system includes a tube that has a first endconnected to the furnace system downstream of an outlet of a combustionair blower and a second end connected to the furnace system upstream ofan inlet of the combustion air blower. An air bleed orifice is throughthe tube. A sensor detects a gas concentration. The sensor is incommunication with flue gas. A controller is in communication with thesensor. The controller monitors the gas concentration.

A furnace system that performs combustion is further provided. Thefurnace system includes a tube having a first end connected to thefurnace system downstream of an outlet of a combustion air blower and asecond end connected to the furnace system upstream of an inlet of thecombustion air blower. The tube has a length minimizing a heat transferarea of the tube in contact with a flue gas. A sensor detects a gasconcentration. The sensor is in communication with a flue gas. Acontroller is in communication with the sensor. The controller monitorsthe gas concentration.

The sensor may be a gas sensor or detector that is selected from thegroup consisting of a metal oxide sensor, a mixed metal oxide sensor, anelectrochemical sensor, an infrared sensor, a catalytic sensor, and anycombination thereof. The sensor may have at least a portion incommunication with the flue gas that recedes, extends into, or remainsflush with a flue elbow. The baffle plate may connect to a flue elbowforming a baffle inlet between the baffle plate and the flue elbowupstream of the sensor and form a baffle outlet between the baffle plateand the flue elbow downstream of the sensor. The baffle plate and a flueelbow may have a volume therebetween. The baffle plate may createnegative pressure in the volume by the Bernoulli effect. The sensor maybe positioned upstream of the draft safeguard switch port relative to aflow of the flue gas. The dilution air may enter the furnace system sothat the baffle plate directs a first portion of the dilution air awayfrom the sensor and a second portion of the dilution air may be directedtoward sensor. At least a portion of the dilution air may mix with aportion of flue gas. The controller may take a control action ordeactivate the furnace system when a preselected gas concentration isdetected by the sensor. The sensor may be redundant to or replace apressure switch of the system. The sensor may be temperature dependentor thermally sensitive and may replace a blocked vent system.

The air bleed orifice may vent an air bleed stream into the tube. Theair bleed orifice may be a metered orifice. The air bleed orifice may beadjacent the first end upstream of the sensor relative to a direction ofa flue sample flow in the tube. The flue gas sample may mix with airfrom the air bleed prior to and during contact with the sensor. Thecombustion air blower may generate a lower pressure at the combustionair blower inlet relative to the combustion air blower outlet to createa vacuum in the tube. The vacuum may direct a flue gas sample past thesensor back into the furnace system. The sensor may be a gas sensor ordetector selected from the group consisting of a metal oxide sensor, amixed metal oxide sensor, an electrochemical sensor, an infrared sensor,a catalytic sensor, and any combination thereof. The controller may takecontrol action or deactivate the furnace system when a preselected gasconcentration is detected by the sensor.

The controller may deactivate the furnace system or take othercorrective action when a preselected gas concentration is detected bythe sensor. The length may be less than about 2.5 inches.

The above-described and other features and advantages of the presentdisclosure will be appreciated and understood by those skilled in theart from the following detailed description, drawings, and appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a front perspective view of a furnace system having a firstexemplary embodiment of a sensor of the present invention;

FIG. 1B schematically depicts an upward perspective view of a flue elbowwith the sensor of FIG. 1A;

FIG. 1C schematically depicts a side cross-sectional view of a flueelbow with the sensor of FIG. 1A;

FIG. 1D schematically depicts a sectional side cross-sectional view of aflue elbow with the sensor of FIG. 1A;

FIG. 2 is a graphical depiction of a comparison of a sensor signal whensampling furnace gas at normal and high carbon monoxide concentrationsat the sensor of FIG. 1C, FIGS. 3A, and 4A;

FIG. 3A schematically depicts the furnace system with a second exemplaryembodiment of a sensor, utilizing an air bleed hole concept and tube todrive flow, reduce sample gas temperature and water vapor content;

FIG. 3B is a side perspective view of the furnace with the sensor ofFIG. 3A;

FIG. 4A schematically depicts the furnace system with a third exemplaryembodiment of a sensor, utilizing a tube concept to reduce sensortemperature, and drive flow;

FIG. 4B schematically depicts a sectional side perspective view of thefurnace system with the sensor of FIG. 4A;

FIG. 4C schematically depicts a sectional side perspective view of thefurnace system with the sensor of FIG. 4A; and

FIG. 4D schematically depicts the furnace system with the sensor of FIG.4A.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIGS. 1 through 4D, an exemplary embodiment of a sensorgenerally referred to by reference numeral 100 is illustrated. Sensor100 detects gas concentration to aid in identifying an incompletecombustion event. Once the combustion event is identified by sensor 100,an appliance, such as, for example, a combustion appliance or an oilburning product may take a control action or shutdown to permit serviceto be performed or an external cause corrected.

Sensor 100 may be any sensor that detects flue gas concentration levels,such as, for example, a gas sensor or detector such as a metal oxide,mixed metal oxide, electrochemical, infrared or catalytic sensor. Sensor100, preferably, is inexpensive as compared with a commercial analyzer.

Sensor 100 may be used in combination with a programmable machine and/orsoftware, more preferably a computer program product having a computeruseable signal with a computer readable code means embodied in themedium designed to monitor a signal from sensor 100. The programmablemachine and/or software may take action as required, such as, forexample, deactivating the gas combustion appliance or oil burningproduct to permit service to be performed or the external causecorrected when sensor 100 exceeds a predetermined concentration of gas.The gas constituent monitored may be the concentration of oxygen, carbondioxide, carbon monoxide, or hydrocarbons. The predeterminedconcentration of gas, for example, carbon monoxide, may be greater than50 parts per million (ppm). One example of a programmable machine is aCPU 500 that is described herein by way of example as a controlprocessing unit. Of course, it is contemplated by the present disclosurefor CPU 500 to include any programmable circuit, such as, but notlimited to, computers, processors, microcontrollers, microcomputers,programmable logic controllers, application specific integratedcircuits, and other programmable circuits. It is further contemplated bythe present disclosure that CPU 500 is any number of control devicesproviding various types of control, e.g., centralized, distributed,redundant and/or remote control. This CPU could be connected to afurnace control board or remotely connected to a thermostat or otherelectronics. The CPU may be integral to the sensor itself.

Referring to FIGS. 1A through 1D, sensor 100 may be used in a furnacesystem 10 to detect flue gas concentration levels. Sensor 100 is locatedinside a flue elbow 15 of furnace system 10. However, sensor may bepositioned anywhere in system 10 that is in communication with flue gas.Sensor 100 extends through a pipe wall of flue elbow 15 with a first endoutside of flue elbow 15 and an opposite second end that extends intoflue elbow 15. However, the sensor 100 may recede, extend into, orremain flush with the flue elbow 15. The sensor 100 is in communicationwith the flue gas. The first end of sensor 100 has a sensor signal wire102 that connects to a CPU 500, as shown in FIG. 1D.

Sensor 100 may have a filter cap 115, as shown in FIGS. 1C and 1D.Filter cap 115 may act as an insulator to insulate sensor 100 from heat.Filter cap 115 minimizes or eliminates transfer of heat from the fluegas to sensor 100 to maintain sensor 100 within a desired operatingtemperature range. The particular type, including materials, dimensionsand shape, of filter cap 115 that is utilized can vary according to themanufacturer, particular needs of sensor 100 and the environment createdby furnace system 10. Filter cap 115, preferably, is non-metallic toprovide insulation rather than conduction of heat, and more preferably,plastic. Insulating sensor 100 with filter cap 115 may extend thelifetime of sensor 100.

Baffle plate 105, preferably, extends from flue elbow 15. Baffle plate105 directs flue gas from flue elbow 15 so that a portion of the fluegas passes below, and in contact with, sensor 100 as illustrated byarrows A in FIG. 1C. Baffle plate 105 directs a remainder of flue gasthrough elbow 15 in a direction away from sensor 100, as shown byreference arrow B in FIG. 1C. Baffle plate 105 may be connected to anyportion of the system 10 in order to direct flue gas around sensor 100.Preferably, the portion of the flue gas that comes into contact withsensor 100 is smaller than the portion of the flue gas directed awayfrom sensor 100. Baffle plate 105, preferably, connects to flue elbow 15on opposite sides of sensor 100 and extends above sensor 100 to form aninlet 120 between baffle plate 105 and flue elbow 15 upstream of sensor100 and an outlet 125 between baffle plate 105 and flue elbow 15 aboveor downstream of sensor 100, as illustrated in FIG. 1C. The baffle plate105 directs flow of flue gas. The flow of the flue gas across the baffleplate 105 creates the conditions for the Bernoulli effect. The Bernoullieffect creates a negative pressure in a volume directly beneath baffleplate 105. The negative pressure induces the flue gas under baffle plate105 into contact with sensor 100. Thus, sensor 100 may detect the gasconcentration of the flue gas without the use of tubing or a sample pumpby taking advantage of the negative pressure created by the Bernoullieffect.

Preferably, a draft safeguard switch permits dilution air to enterthrough a draft safeguard switch port 20 as illustrated by arrow C inFIG. 1C. Sensor 100, preferably, is positioned upstream of draftsafeguard switch port 20 relative to the flow of the flue gas. Thedilution air may enter flue elbow 15 between flue elbow 15 and baffleplate 105 so that a first portion of the dilution air is directed awayfrom sensor 100, as illustrated by arrow J in FIG. 1D, and a secondportion of dilution air is directed toward sensor 100, as illustrated byarrows D in FIG. 1D. As illustrated by arrows A and J between sensor100, baffle plate 105, and flue elbow 15, the dilution air and flue gasmix. The dilution air of draft safeguard switch port 20 acts to reducethe sensor temperature surrounding sensor 100 and may extend thelife-span of sensor 100 when compared with a sensor exposed to undilutedflue gas. Sensor 100 may also have a lowered humidity compared with asensor exposed to undiluted flue gas as a result of the dilution air.The lower flue gas humidity created by the dilution air may alsoincrease the life-span of sensor 100.

The location of sensor 100 inside flue elbow 15 near draft safeguardswitch port 20 under the baffle plate 105 minimizes condensation bytaking advantage of a flue gas temperature at that location and thedilution air entering flue elbow 15 through draft safeguard switch airport 20. Thus, sensor 100 may be directly exposed to the diluted fluegas inside flue elbow 15 at the operating temperature range that sensor100 is able to reliably function and eliminates any need for a sampletube, separate or parallel gas circuit, sample pump, or other analogouspath located outside of a flue gas path to transport a flue gas samplestream from the flue gas path to a sensor.

Sensor 100 may be temperature dependent and may be used to replace theblocked vent system. Temperature and humidity may be parameters detectedby sensor 100. The temperature and humidity dependencies of sensor 100can be taken advantage of to calculate a flue gas temperature aroundsensor 100 by CPU 500 or other control device. Upon sensor 100 detectinga predetermined temperature, the blocked vent system may be activated ordeactivated.

Sensor 100 may also be used to replace or provide redundancy to thepressure switch. Currently the pressure switch is used to ensure aproper amount of combustion air is supplied to a combustion process. Iftoo little combustion air is supplied to the combustion process,elevated flue gas carbon monoxide concentrations compared with typicaloperating conditions undesirably result. Alternatively, if too muchcombustion air is supplied, elevated carbon monoxide concentrationsresult, a gas concentration sensor would sense high concentrations ofcarbon monoxide or other gas and take control action or deactivate thefurnace.

Referring now to FIGS. 3A and 3B, sensor 100 may be used with a smalltube or separate or parallel gas circuit 200. Gas circuit 200 may have asample tube 205. Sample tube 205 may have a first end 207 connected to afirst combustion air blower outlet 30 of a flue gas blower or combustionair blower 35 of furnace system 10. Sample tube 205 may have a secondend 209 opposite first end 207 connected to a combustion air blowerinlet 40 of combustion air blower 35. Sample tube 205 may have an airbleed orifice 210. Air bleed orifice 210, preferably, is a meteredorifice to control an inflow or bleed air.

The particular type, including materials, dimensions and shape, ofsample tube 205 and air bleed orifice 210 that is utilized can varyaccording to the particular needs of sensor 100 and furnace system 10. Asilicone tube one quarter inch in outside diameter is preferred but itcould be made from any variety of materials such as copper, or stainlesssteel. Any diameter or shape may Uncork but a smaller diameter tube ispreferred.

The combustion air blower 35 generates a lower pressure at combustionair blower inlet 40 relative to combustion air blower outlet 30, thus,creating a vacuum. The vacuum creates a direction of flow, asillustrated by arrow F, that directs a flue gas sample into sample tube205 of gas circuit 200. An inflow or air bleed, as illustrated by arrowG, of air from outside of sample tube 205 may enter sample tube 205through air bleed orifice 210. Air bleed orifice 210, preferably, isupstream, relative to the direction of flow illustrated by arrow F, ofsensor 100 to mix the flue gas sample with air from the air bleed priorto and during contact with sensor 100. The flue gas sample flows in adirection shown by arrow H into contact with sensor 100. The vacuumcreated by combustion air blower 35 directs flue gas sample past sensor100 back into furnace system 10, as shown by arrow I. Thus a gas samplepump, is not required to direct flow to sensor 100.

An air bleed airflow rate may be more controlled and less variable thanother prior art flue gas dilution. The air from the airbleed that maymix with the flue gas may lower the humidity and temperature of the fluegas sample. Thus, the air bleed airflow functions to lower the sensortemperature and humidity compared to a sensor exposed to undiluted fluegas. The air bleed may also assist in preventing a condensate blockagein sample tube 205. The air bleed may maintain a small flow of airthrough sample tube 205 that evaporates and assists movement and removalof condensate water. If air bleed orifice 210 has a diameter that isprecisely manufactured, an airflow rate into sample tube 205 can bequantified and proportions of the flue gas and air in sample tube 205may be adjusted for optimal function of sensor 100. Sample tube 205 mayalso be insulated to maintain an average temperature of gases passingthrough sample tube 205 above the dew point temperature to furtherminimize condensate water.

FIG. 2 illustrates a graphical depiction of a comparison of a sensorsignal when sampling furnace gas at normal and high carbon monoxideconcentrations at sensor of FIG. 1C, FIGS. 3A, and 4A described below.

Referring now to FIGS. 4A through 4D, sensor 100 may be used with a gascircuit 300 that is similar to gas circuit 200 described above withoutair bleed orifice 210. Gas circuit 300 may have a short tube 305. Shorttube 305 may have a first end 307 connected to combustion air bloweroutlet 30 of combustion air blower 35 of furnace system 10. Short tube305 may have a second end 309 opposite first end 307 connected to acombustion air blower inlet 40 of combustion air blower 35.

The combustion air blower 35 generates a lower pressure at combustionair blower inlet 40 relative to combustion air blower outlet 30, thus,creating a vacuum. The vacuum creates a direction of flow, asillustrated by arrow F, that directs flue gas sample into short tube 305of gas circuit 300. The flue gas sample flows in a direction shown byarrow H into contact with sensor 100. The vacuum created by combustionair blower 35 directs flue gas sample through short tube 305 past sensor100 into a collector box 45 of furnace system 10, as shown by arrow I.Thus a sample pump is not required to direct flow to sensor 100. Shorttube 305 reduces a probability of condensate blockage in the flue gassample. If short tube 305 is preferably less than 2.5 inches, but may beshorter or longer, the heat transfer area of short tube 305 in contactwith the flue gas sample is limited; and, thus, condensate blockage islimited. The gas concentration detected by sensor 100 can be used by CPU500 to determine if the gas concentration exceeds a maximum permittedconcentration, in which case CPU 500 may shut off fuel gas to furnacesystem 10 or take other appropriate action for proper combustionperformance.

While the instant disclosure has been described with reference to one ormore exemplary embodiments, it will be understood by those skilled inthe art that various changes may be made and equivalents may besubstituted for elements thereof without departing from the scopethereof. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of the disclosurewithout departing from the scope thereof. Therefore, it is intended thatthe disclosure not be limited to the particular embodiment(s) disclosedas the best mode contemplated for carrying out this invention, but thatthe invention will include all embodiments falling within the scope ofthe appended claims.

What is claimed is:
 1. A furnace system that generates heat bycombustion, the furnace system comprising: a sensor that detects a gasconcentration of a flue gas, said sensor being positioned in a flueelbow in communication with said flue gas, said sensor generating asensor signal, the sensor having a filter cap for providing insulationto said sensor; a controller in communication with said sensor, saidcontroller monitoring said gas concentration; a baffle plate directing afirst portion of said flue gas into contact with said sensor and asecond portion of said flue gas in a direction away from said sensor;and a draft safeguard switch port located in the elbow having a draftsafeguard switch that selectively permits dilution air to enter thefurnace system to mix with said first portion of said flue gas; whereinsaid baffle plate connects to a flue elbow forming a baffle inletbetween said baffle plate and said flue elbow upstream of said sensorand forming a baffle outlet between said baffle plate and said flueelbow downstream of said sensor.
 2. The system of claim 1, wherein saidsensor is a gas sensor or detector selected from the group consisting ofa metal oxide sensor, a mixed metal oxide sensor, an electrochemicalsensor, an infrared sensor, a catalytic sensor, and any combinationthereof.
 3. The system of claim 1, wherein said sensor has at least aportion in communication with flue gas that recedes, extends into, orremains flush with a flue elbow.
 4. The system of claim 1, wherein saidbaffle plate and a flue elbow have a volume therebetween.
 5. The systemof claim 1, wherein said sensor is positioned upstream of said draftsafeguard switch port relative to a flow of said flue gas.
 6. The systemof claim 1, wherein said dilution air enters the furnace system so thatsaid baffle plate directs a first portion of said dilution air away fromsaid sensor and a second portion of said dilution air is directed towardsensor, and wherein at least said second portion of said dilution airmixes with said first portion of flue gas.
 7. The system of claim 1,wherein said controller takes a control action or deactivates thefurnace system when a preselected gas concentration is detected by saidsensor.
 8. The system of claim 1, wherein said sensor is redundant to orreplaces a pressure switch of the system.
 9. The system of claim 1,wherein said sensor is temperature dependent or thermally sensitive andreplaces a blocked vent system.
 10. A furnace system that generates heatby combustion, the furnace system comprising: a tube having a first endconnected to the furnace system downstream of an outlet of a combustionair blower and a second end connected to the furnace system upstream ofan inlet of said combustion air blower; an air bleed orifice throughsaid tube; a sensor that detects a gas concentration, said sensor beingpositioned in said tube in communication with flue gas, said sensorgenerating a sensor signal, wherein said sensor is a gas sensor ordetector selected from the group consisting of a metal oxide sensor, amixed metal oxide sensor, an electrochemical sensor, an infrared sensor,a catalytic sensor, and any combination thereof; and a controller incommunication with said sensor, said controller receiving said sensorsignal for monitoring said gas concentration.
 11. The system of claim10, wherein said air bleed orifice vents an air bleed stream into saidtube.
 12. The system of claim 10, wherein said air bleed orifice is ametered orifice.
 13. The system of claim 10, wherein said air bleedorifice is adjacent said first end upstream of said sensor relative to adirection of a flue sample flow in said tube, and wherein said flue gassample mixes with air from said air bleed prior to and during contactwith said sensor.
 14. The system of claim 10, wherein said combustionair blower generates a lower pressure at said combustion air blowerinlet relative to said combustion air blower outlet to create a vacuumin said tube, and wherein said vacuum directs a flue gas sample pastsaid sensor back into the furnace system.
 15. The system of claim 10,wherein said sensor is a gas sensor or detector selected from the groupconsisting of a metal oxide sensor, a mixed metal oxide sensor, anelectrochemical sensor, an infrared sensor, a catalytic sensor, and anycombination thereof.
 16. The system of claim 10, wherein said controllertakes control action or deactivates the furnace system when apreselected gas concentration is detected by said sensor.
 17. A furnacesystem that performs combustion, the furnace system comprising: a tubehaving a first end connected to the furnace system downstream of anoutlet of a combustion air blower and a second end connected to thefurnace system upstream of an inlet of said combustion air blower, saidtube having a length minimizing a heat transfer area of said tube incontact with a flue gas; a sensor that detects a gas concentration, saidsensor being positioned in said tube in communication with a flue gas,said sensor generating a sensor signal, wherein said sensor is a gassensor or detector selected from the group consisting of a metal oxidesensor, a mixed metal oxide sensor, an electrochemical sensor, aninfrared sensor, a catalytic sensor, and any combination thereof; and acontroller in communication with said sensor, said controller receivingsaid sensor signal for monitoring said gas concentration.
 18. The systemof claim 17, wherein said controller deactivates the furnace system ortakes other corrective action when a preselected gas concentration isdetected by said sensor.
 19. The furnace system of claim 1 wherein saidbaffle plate has a geometry that divides the flue gas into separatestreams and permits said separate streams to rejoin downstream of saidbaffle plate.